In all likelihood, there are not only multiple universes, but an infinite number of them. This is what most versions of eternal inflation entail. The evidence for inflation grows stronger every year, and eternal inflation is the most likely variety of it.

Greene’s book explores half a dozen versions of the multiverse (multiple, or parallel, universes), and most of them are not mutually exclusive. There could be several flavors of parallelism at work simultaneously.

One likely aspect of the multiverse is what Greene calls the Swiss cheese model, in which our universe is like one of the bubbles in a block of Swiss cheese. The block has always existed, and has always been infinite in extent. (To those who ask, “Where did it come from?” I would reply, “Why should nothing be the default state? If there were nothing, we would be asking, ‘Who took everything away?’ …except we would not be here to ask that.”) The block expands due to processes that I only started to understand on this reading of the book and which I won’t attempt to explain here. In fact, it has always been expanding (but has always been infinite — infinity is a strange thing). Once in a while, a quantum fluctuation causes a “bubble” to form, one of which is our universe. These bubbles are carried away from each other in the expanding block, keeping them as isolated and distinct universes.

Because this has been happening forever, the number of bubble universes is already infinite. An infinite number are yet to come.

This post is not about how all that might work. For now, I only want to dwell on why I find this idea of infinite universes so comforting.

To appreciate it, you first must grasp just what infinity entails. Think of repeating an experiment an infinite number of times. If your experiment is to roll a pair of dice, then every possible outcome would happen at least once. In fact, it would happen an infinite number of times. Double-sixes? An infinite number of them. That’s amazing, but we’re just getting started.

Suppose your experiment is to thoroughly shuffle a deck of cards. Any outcome you can think of will be represented, including the outcome of the deck sorted just as it was when the box was opened: all the spades, followed by all the diamonds, clubs and hearts, and sorted by rank within suit. In fact, that will happen an infinite number of times. It’s harder to believe than getting an infinite number of double-sixes, but it’s true for exactly the same reason. Infinity is really big!

It’s so big that if instead of dice or cards, you were to play with a finite number of atoms arranged in a finite space, then every physically possible arrangement would be among the outcomes of the experiment. What is our universe, but a finite number of atoms in a finite space? Yes, if there are infinitely many universes, then others exactly identical to ours appear an infinite number of times (assuming, Greene hastens to add, that there’s nothing special about ours, and there is no reason to think there is).

Not only that, but there are others identical to ours except for that one detail of ours that bothers you the most.

That is the first comfort: If things have gone badly here, there’s a universe where they went well. An infinite number of them, in fact.

Of course, there’s also a place where they went much, much worse, so in case you’re a glass-half-empty sort of person let’s turn to the second comfort.

The nice thing about eternal inflation is that it will go on without us. Not only that, but when our universe has finally turned cold and dark, other universes will just be getting started, while in others the first life-forms will be starting to stir, just beginning their billion-year climb up the evolutionary ladder first to sentience, then to full awareness of their world, and finally to awestruck wonder at the universe they inhabit.

Why is this a comfort? Sometimes I feel responsible for so much. I have a family that is undergoing a lot of stress at the moment, a job in which I’m behind schedule, a book I’m writing, and even a musical instrument I have neglected for several months. I take my responsibilities seriously, but it’s nice to know that regardless of how well or poorly I do, the multiverse will go on without me.

It does not all depend on me or on you, even though sometimes it feels that way.

Look to the sky on the darkest, starriest night. Think about everything you see repeated in every possible variation, an infinite number of times. Think about the entire history of this universe, again repeated with infinite variations, more beautiful than the simultaneous play of a million kaleidoscopes. To think that all that beauty will continue to multiply with or without you … doesn’t that lighten the load?

What if the truth about life were horrible? What if, as the ancient Hebrews believed, we are all destined to spend eternity in a shadowy sheol rather than a glorious heaven? Or what if there is no afterlife at all? What if life is absurd — just a cosmic joke played on us by no-one at all?

If you were to discover that any of these propositions is absolutely, undeniably true, how would you feel?

I’ve been rereading Plato at the Googleplex, in which author Rebecca Goldstein imagines Plato on a book tour in modern America. I’d like to share with you a passage that I find very moving. Ms. Goldstein, synthesizing Plato’s writings, has him say this about those who are fit to be the Guardians of his ideal republic.

[An essential character quality is] an inborn horror of being deceived as to the nature of things, and an inborn desire to know the truth… [It] is something different from intelligence and different from knowledge. Those who have this trait love the truth not because it is like this or like that. They love the truth simply because it is the truth and are prepared to love it no matter what it turns out to be. They will stick to a view just so long as it seems to them the truth and will not be seduced away from that view no matter what others are telling them, or what flashier and more attractive options are dangled before them; but they are also the least reluctant among all people to abandon a formerly loved view, if once they become convinced that it is not true. They are always on the scent of the truth, like dogs, who are the most philosophical of animals.

Do you identify with this? I do. During the years that I was in the evangelical church, nothing “seduced me away from that view” — not money, not social opportunities, not fleshly lusts, not even the common decency to see some of its teachings as horrible. I thought I had found the truth; how could anything else matter?

I’ve been collecting and posting tests of how much one loves truth, as proposed by famous philosophers. So far, we have

Plato’s test: Tell children glorious stories. Emphasize that the stories are true when they are, in fact, false. See which children can resist the stories’ appeal, and spontaneously protest as to why they are impossible.

C.S. Lewis’ Test: Upon learning that an ugly rumor about one’s enemies is false, is one relieved that even they aren’t as bad as all that, or does one wish to cling to the rumor?

Now for Voltaire’s.

For my entire adult life, this writer of the French Enlightenment was reviled as an enemy of God by every one of my acquaintances who was educated enough to recognize his name. I formed the impression that he was a villain who, entirely unprovoked, spent his bitter life writing polemics against Christianity.

Imagine my curiosity when I read Robert Ingersoll‘s Lecture on Voltaire, and learned that he was exceedingly generous and warm-hearted, a tireless advocate of liberty and justice, and may have done more than anyone else to abolish cruel and unusual punishments in France.

I decided to read the first of his works that I could get my hands on, and that happened to be Candide. In this book, the guileless Candide is raised in a castle and tutored by the philosopher, Pangloss, whose most memorable tenet is that we live in the best of all possible worlds. (“It is demonstrable,” said he, “that things cannot be otherwise than as they are; for as all things have been created for some end, they must necessarily be created for the best end. Observe, for instance, the nose is formed for spectacles, therefore we wear spectacles.”)

Almost from page 1, bad things begin to happen to Candide and everyone else in the castle, from which they are all driven out. Candide, separated from Pangloss for most of his tribulations, wonders whether the philosopher would maintain his sunny outlook in the face of so much distress.

Pangloss returns at the end of the book, having suffered at least as much as Candide.

Candide asks him, “When You were hanged, dissected, whipped, and tugging at the oar [as a galley slave], did you continue to think that everything in this world happens for the best?”

“I have always abided by my first opinion,” answered Pangloss; “for, after all, I am a philosopher, and it would not become me to retract my sentiments; especially as Leibnitz could not be in the wrong: and that preestablished harmony is the finest thing in the world.”

In the final chapter, Candide and Pangloss are living a quiet life on a small farm. Pangloss tries to convince Candide that Candide’s misfortunes, which were many and severe, are entirely compatible with this being the best of all possible worlds. “For had you not suffered them,” Pangloss says, “you would not have been here to eat preserved citrons and pistachio nuts.”

Obviously and comically, the pleasures of citrons and pistachio nuts are as nothing compared to what both men have suffered. But they are all Pangloss needs to hold onto his doctrine.

I suppose there are many truth-loving tests one could extract from this book, but I’ll choose this one:

Our love of truth is inversely related to our stubbornness in holding onto our ideas, and the lameness of our rationales, as judged by an impartial, educated observer.

One of my kids asked me today, “How can a person prevent herself from being prejudiced? I have a bad impression of the culture of [a certain country], and when I meet someone from there, it’s very hard not to assume he’s like that.”

One strategy that arose in our conversation was to remember what “bad” groups we are members of, and how we don’t conform to the stereotypes.

We’re American and I imagine the picture the rest of the world has of us. Compared to most developed countries, we have far more crime, yet we insist on having permissive gun-ownership laws; we have more people in prison than any country on Earth, yet we style ourselves as the moral beacon of the world; our government is incredibly dysfunctional when it comes to caring for the poor, but we always seem to have enough money to invade other countries; we want the world to trust our leadership, but we spy even on our friends; we like to tell other countries to respect their citizens’ rights and the rights of their neighbors, yet it was not all that long ago that we stole the bulk of our continent from Native Americans and Mexico; we are the only country ever to have have used a nuclear weapon in war, and we have done it twice; our academic scores are well behind many less-developed countries’ and we seem determined to remain ignorant, with large numbers of us denying climate change and evolution. I could go on and on.

Yet, if you meet an American on the street, chances are he’s a normal, nice person with a decent moral core.

Sometimes, our prejudice toward someone arises from assuming he will live up to the dangerous implications of his ideology. But most people don’t. Most people quietly ignore those parts of their belief system that are particularly bad.

They have learned to do so because they are carried along by a civilization that has moved on from the early days of their ideologies. You won’t find Jews today in favor of slavery or genocide even though God commandedboth in the Hebrew Bible. Christians don’t torture people into professing orthodox faith anymore even though they once thought it a good idea since an eternity in heaven or hell was in the balance.

If we are open to the possibility that other people don’t conform to their stereotypes any more than we do to ours, I think most people will pleasantly surprise us.

What I proposed was having our children be told glorious tales to stir their imaginations, very much stressing all the time that these tales were true, and then seeing which among the children can resist them, can see the logical inconsistencies within these tales, and see all their inconsistencies with other truths that they have been told.

Here’s another truth-loving test, from C.S. Lewis’s book, Mere Christianity. (In the book, he did not propose this as a truth-loving test, but I think it makes an excellent one.)

The real test is this. Suppose one reads a story of filthy atrocities in the paper. Then suppose that something turns up suggesting that the story might not be quite true, or not quite so bad as it was made out. Is one’s first feeling, “Thank God, even they aren’t quite so bad as that,” or is it a feeling of disappointment, and even a determination to cling to the first story for the sheer pleasure of thinking your enemies are as bad as possible?

I read the quote over at Slacktivist’s blog. He had earlier treated the theme in a wonderful post called Jackie at the crossroads. In that story, a young woman named Jackie has claimed there are poisonous spiders in airport restrooms, former stow-aways on international flights. When she is shown that this is just an urban legend, she has a choice: she can double-down or laughingly admit her gullibility. Her choice is a very clear window on her character.

How about us? When we learn that the rumor we have spread about our political or religious adversaries is unfounded, is our first reaction to be relieved that they are not so bad after all? Or do we double down by finding another way they are so bad, or by calling the refutation “biased” even though it is our own bias that has just been exposed?

The Copernican view was finally accepted, but we still thought we were exceptional because the laws of physics were different on Earth than in the heavens. Isaac Newton changed all that. In 1687, he publishedMathematical Principles of Natural Philosophy, proving that a single Law of Gravity could explain movements in both heaven and Earth.

In 1920, we learned that, not only were we not at the center of the solar system, but our solar system was not at the center of our galaxy. Later in that decade, we would learn that our galaxy was but one among many.

Close on the heels of that discovery, Edwin Hubble proved that the universe is expanding. We were becoming a smaller part of the whole all the time. And at an accelerating rate: at the close of the century, we realized that the universe is flying apart faster and faster.

Working the expansion backward, Alexander Friedmann had suggested, in 1922, that the universe could have been born in what we now call the Big Bang. Even Einstein initially called the idea “suspicious” but by mid-century, it had begun to take hold. Apparently we are even less than the dust of the Earth: we are detritus from a random quantum fluctuation.

In 1600, Giodano Bruno got himself burned at the stake for, among other heresies, suggesting that the stars were suns much like ours, with inhabited planets. It was not until the time of America’s Civil War that conclusive proof was found that he was right about the suns, and not until after the first Gulf War that he was right about the planets.

When I was a schoolboy, I was taught that our world was almost certainly the only inhabited one in the universe. The scientific consensus now seems to be that life on other worlds is inevitable.

I was also taught humans were the only animals who could reason or use tools. I just finished a book about an African Grey parrot who could hold an intelligent conversation, in English, infused with a mischievous sense of humor. Many species have been observed not only to use but to make tools.

Our self-concept has come a long way from being the apex of creation, in a domed terrarium made especially for us to inhabit, only a few thousand years ago. We now know we are specs on a pale blue dot that orbits a larger, white dot that occupies a not-so-special place two thirds of the way down one of the spiral arms of a galaxy that has, at its center, a supermassive black hole.

Coming toward us at 110 kilometers per second is the Andromeda galaxy — three times as large at the Milky Way and with its own supermassive black hole. Fortunately, space is so vast that it will be 4 billion years before the galaxies collide. Our best guess is that when they do, the Earth will first be pulled toward the dual black holes and then ejected to intergalactic space.

But nobody will be here to witness Earth’s ignominious end. Three billion years earlier (only a billion from now) the radiation from the Sun will have grown so intense that it will have extinguished the last spark of life on our planet.

Life was born here 3.5 billion years ago, and has less than 1 billion to go. Now that we are well past middle age, perhaps it is time to reflect on our accomplishments.

If we can be proud of anything, it is this: that we have discovered the vastness of space and time in the universe, and our correspondingly humble position in it. After centuries of fighting against our change in circumstance, we may also be proud of having exchanged our offense for awe.

Just when you think you have one universe down pat, along come infinity more.

It’s unlikely that I will live to see any of those multiverse theories proven or disproven, but who knows — when my grandparents were born, the existence of other galaxies beyond our Milky Way was not even known. If our knowledge could expand from one galaxy to over 176 billion in less than a hundred years, maybe one additional universe will show up any day now.

We made this progress because we never stopped asking questions. When we found an answer, we said, “Fine. What’s next?”